1. Field of the Invention
The present invention relates to a signal transmission circuit, an integrated circuit and an electric device including thereof, and more particularly to a signal transmission technique for a plurality of signals each having a different transmission speed.
2. Description of the Background Art
There has been known a method for transmitting a pulse signal generated based on a signal to be transmitted, by using a pulse transformer, a photocoupler or the like, when transmitting an electrical signal in a mutually electrically insulated manner.
Japanese Patent Laying-Open No. 2010-10762 (PTD 1) discloses a signal transfer circuit device used in a drive circuit device for a power semiconductor, the signal transfer circuit device transferring a control input signal by using a pulse transformer and including a self-diagnosis functional block for detecting and monitoring whether a transmitted signal is restored faithfully to the control input signal or not.
A method for transmitting a single digital signal by using an insulating element such as the pulse transformer or the photocoupler as described above includes a method for transmission with an oscillating pulse of a prescribed cycle by using one insulating element, and a method for transmitting a pulse based on rising and falling edges of a signal to be transmitted, by using two insulating elements.
In the case of transmitting two signals each having a different transmission speed, it is conceivable to use a combination of the aforementioned configurations for transmitting a single signal. However, if signal transmission is implemented by a simple combination of a plurality of signal transmission circuits, the number of components increases, which may lead to constraint on size reduction and increase in cost. Alternatively, when the signal transmission circuit using the oscillating pulse is utilized in the case of transmitting a signal having a high transmission speed, it is necessary to shorten the oscillation cycle, that is, to use the signal to have a higher frequency in order to prevent a delay in transmission caused by the oscillation cycle. Therefore, the power for an oscillation circuit increases, which may lead to decrease in efficiency of the entire circuit.
The present invention has been made to solve the aforementioned problem, and an object thereof is to provide a signal transmission circuit capable of transmitting a plurality of signals each having a different transmission speed in a mutually electrically insulated manner, by using a comparatively simple circuit.